Here's why:

* Plate Tectonics: Mid-ocean ridges are formed at divergent plate boundaries where tectonic plates move apart. This process happens across the globe.

* Global System: The mid-ocean ridge system is actually a single, continuous chain of mountains that wraps around the globe. It's the longest mountain range on Earth!

* Major Ocean Basins: Each major ocean basin (Atlantic, Pacific, Indian, Arctic, and Southern) contains segments of the mid-ocean ridge system.

So, while the exact locations and characteristics of the ridges vary between oceans, they are a fundamental feature of all of them.